Ultra broadband network of fixed or switched frequency selective filters

ABSTRACT

An extensible filter structure is disclosed allowing realizable effective filtering over many decades in frequency. Multiple devices operating with mismatched frequency ranges can be multiplexed together with or without switching.

TECHNICAL FIELD

The systems described herein generally relate to an electrical circuitthat utilizes a plurality of diplexers.

BACKGROUND

Conventional wideband switching networks have been designed to steersignals through appropriate narrower band filters. Each filter isaccessed individually according to the switch settings. As the number offilters increases, the switching losses increase correspondingly.

Conventional diplexer structures are not generally considered to haveacceptable performance over a wide frequency band (greater than onedecade in frequency). Some cascaded diplexers can allow realizableconcurrent frequency selective filtering over 4 decades in frequency.

Networks that combine bandpass filters into a broader band common portexist. One example is a log periodic antenna that combines multiple bandpass antenna elements into a broader contiguous frequency band inparallel along a transmission line. Antenna multicouplers typically useseveral bandpass filters in parallel to combine several radios to asingle antenna. The parallel arrangement means the undesired resonancesare not decoupled from the output.

The novel filter network arrangement disclosed, allows multiple filtersto be accessed concurrently. Additionally, switching may be embeddedinside the filter network, avoiding the cascaded switching losses.

SUMMARY

In accordance with one embodiment, an electrical circuit comprises afirst diplexer and a second diplexer. The first diplexer comprises afirst low pass filter and a first high pass filter. The first low passfilter comprises a first input and a first output. The first low passfilter defines a first low pass cutoff frequency. The first high passfilter comprises a second input and a second output. The first high passfilter defines a first high pass cutoff frequency and the first andsecond inputs are directly electrically coupled together. The seconddiplexer comprises a second low pass filter and a second high passfilter. The second low pass filter comprises a third input and a thirdoutput. The second low pass filter defines a second low pass cutofffrequency. The second high pass filter comprises a fourth input and afourth output. The second high pass filter defines a second high passcutoff frequency. The first output, the third input, and the fourthinput are directly electrically coupled together. The first low passcutoff frequency and the first high pass cutoff frequency aresubstantially the same. The second low pass cutoff frequency is lessthan the first low pass cutoff frequency. The second high pass cutofffrequency is less than the first high pass cutoff frequency. The secondlow pass cutoff frequency and the second high pass cutoff frequency aresubstantially the same.

BRIEF DESCRIPTION OF THE DRAWINGS

It is believed that certain embodiments will be better understood fromthe following description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a schematic block diagram depicting an electrical circuithaving a plurality of diplexers, in accordance with one embodiment;

FIG. 2 is a schematic block diagram depicting an electrical circuithaving a plurality of diplexers, in accordance with another embodiment;

FIG. 3 is a schematic block diagram depicting an electrical circuithaving a plurality of diplexers and terminated filters, in accordancewith one embodiment;

FIG. 4 is a schematic view depicting one example of the electricalcircuit of FIG. 3;

FIG. 5 is a schematic block diagram depicting an electrical circuithaving a plurality of diplexers and A/D converters, in accordance withone embodiment;

FIG. 6 is a schematic block diagram depicting an electrical circuithaving a plurality of diplexers and A/D converters, in accordance withone embodiment;

FIGS. 7-16 depict different plots depicting the frequency response ofthe electrical circuit of FIG. 6 based upon different switchingconditions; and

FIG. 17 is a schematic block diagram depicting a conventional diplexerarrangement.

DETAILED DESCRIPTION

In connection with the views and examples of FIGS. 1-16, wherein likenumbers indicate the same or corresponding elements throughout theviews, an electrical circuit 20 is illustrated in FIG. 1 and is shown toinclude a first diplexer 22 and a second diplexer 24 that areelectrically connected together such that they can be considered“cascaded”. The first diplexer 22 comprises a low pass filter 26 and ahigh pass filter 28. The low pass filter 26 comprises an input 30 and anoutput 32 and defines a low pass cutoff frequency. The high pass filter28 comprises an input 34 and an output 36 and defines a high pass cutofffrequency that is substantially the same as the low pass cutofffrequency of the low pass filter 26. The inputs 30, 34 of the low andhigh pass filters 26, 28 are directly electrically coupled together. Thesecond diplexer 24 comprises a low pass filter 38 and a high pass filter40. The low pass filter 38 comprises an input 42 and an output 44 anddefines a low pass cutoff frequency. The high pass filter 40 comprisesan input 46 and an output 48 and defines a high pass cutoff frequencythat is substantially the same as the low pass cutoff frequency of thelow pass filter 38. The output 36 of the high pass filter 28 of thefirst diplexer 22 is directly electrically coupled with each of theinputs 42, 46 of the respective low and high pass filters 38, 40 of thesecond diplexer 24. One example of a conventional diplexer isillustrated in FIG. 17.

The low pass cutoff frequency of the low pass filter 38 of the seconddiplexer 24 can be less than the low pass cutoff frequency of the lowpass filter 26 of the first diplexer 22. The low pass cutoff frequencyof the low pass filter 38 of the second diplexer 24 can be less than thelow pass cutoff frequency of the low pass filter 26 of the firstdiplexer 22. The high pass cutoff frequency of the high pass filter 40of the second diplexer 24 can be less than the high pass cutofffrequency of the high pass filter 28 of the first diplexer 22. It is tobe appreciated that the high pass and low pass filters 26, 28, 38, 40can be complementary and cascaded in a particular manner to achieve anetwork of filters capable of combining or separating bandlimited signalpaths to or from a common broader bandwidth signal path. Separatedsignal paths can be switched and then recombined to a common signal paththus allowing individual control of each bandlimited signal path betweena single input and output.

If a desired diplexer design becomes sufficiently complex, any of avariety of methods can be employed to dampen undesired resonances. Forexample, realizable, non-ideal inductors and capacitors can beconstructed so that undesired resonances fall well above the cutofffrequency of the filter in which they are used. These resonances cancompromise the broadband performance of the filters if they are used inan externally switched network. These resonances above cutoff inside thenetwork are successively suppressed behind low pass filters havingsuccessively higher cutoff frequencies moving toward the outside of thenetwork. If properly designed, the only resonances measureable will befrom diplexer closest to the outside of the network. This allows thedesigner to make the undesired resonances as high as needed. Computersimulations have demonstrated flybacks above 100 GHz on a filter builtinto an integrated circuit. The filter provides controlled selectivitydown to 0 Hz. Additionally or alternatively resonances from theinteractions between sufficiently complex diplexers can be suppressed byinternal filters having their own terminations. These internallyterminated filters can be connected to the diplexer outputs or beknitted into the diplexer's high pass and low pass ladder structure bysharing a ladder component. Their cutoff frequencies can be well aboveor below the band of the respective signal path to which they areconnected so they cause very little effective loss to the desired signalpaths.

FIG. 2 illustrates an electrical circuit 120 according to anotherembodiment that includes a first diplexer 122, a second diplexer 124,and a third diplexer 150 that are provided in a cascaded arrangement.The first and second diplexers 122, 124 can be similar to or the same asthe first and second diplexers 22, 24 illustrated in FIG. 1. The thirddiplexer 150 can be similar to or the same as either of the first andsecond diplexers 22, 24 illustrated in FIG. 1. A low pass cutofffrequency of a low pass filter 152 of the third diplexer 150 can be lessthan a low pass cutoff frequency of a low pass filter 138 of the seconddiplexer 124. A high pass cutoff frequency of a high pass filter 154 ofthe third diplexer 150 can be less than a high pass cutoff frequency ofa high pass filter 140 of the second diplexer 124. The low pass cutofffrequency of the low pass filter 152 and the high pass cutoff frequencyof the high pass filter 154 can be substantially the same. It is to beappreciated that any quantity of diplexers can be cascaded togethersimilar to FIGS. 1 and 2.

FIG. 3 illustrates an electrical circuit 220 according to anotherembodiment that includes a first diplexer 222 and a second diplexer 224that are provided in a cascaded arrangement. The first and seconddiplexers 222, 224 can be similar to or the same as the first and seconddiplexers 22, 24 illustrated in FIG. 1. The electrical circuit 220however can include a first terminated low pass filter 256, a secondterminated low pass filter 258, a first terminated high pass filter 260,and a second terminated high pass filter 262. The first terminated lowpass filter 256 can be electrically coupled to an output 236 of a highpass filter 228 of the first diplexer 222. The first terminated highpass filter 260 can be electrically coupled to the interconnectionbetween an output 232 of a low pass filter 226 of the first diplexer 222and inputs 242, 246 of respective low and high pass filters 238, 240 ofthe second diplexer 224. The second terminated low pass filter 258 canbe electrically coupled to an output 248 of a high pass filter 240 ofthe second diplexer 224. The second terminated high pass filter 262 canbe electrically coupled to an output 244 of a low pass filter 238 of thesecond diplexer 222. The first terminated low pass filter 256 can have acutoff frequency that is less than the cutoff frequency of the high passfilter 228 of the first diplexer 222. The first terminated high passfilter 260 can have a cutoff frequency that is higher than the cutofffrequency of the low pass filter 226 of the first diplexer 222. Thesecond terminated low pass filter 258 can have a cutoff frequency thatis less than the cutoff frequency of the high pass filter 240 of thesecond diplexer 224. The second terminated high pass filter 262 can havea cutoff frequency that is higher than the cutoff frequency of the lowpass filter 238 of the second diplexer 224.

Singly terminated filters, such as the first and second terminated lowpass filters 256, 258 and the first and second terminated high passfilters 260, 262, can be an optimized class of filters for the high passand low pass filters that constitute the diplexers. Singly terminatedfilters can be designed to be driven from either a voltage or currentsource. Singly terminated filters can consist of series and shuntinductors and capacitors that are arranged in alternating fashion in atwo port ladder network. A voltage source can be connected to the singlyterminated filter using a series inductor or capacitor. A current sourcecan be connect to the singly terminated filter using a shunt inductor orcapacitor. A voltage sourced singly terminated filter can have a highimpedance resisting the flow of current in its rejection band and canallow power to flow from the source to a resistive termination in itspassband. A current sourced singly terminated filter can have a lowimpedance resisting the production of a voltage in its rejection bandand can allow power to flow from the source to a resistive terminationin its passband. Singly terminated high and low pass filters can bedesigned to be voltage sourced with a series inductor or capacitor andcan have equivalent cutoff frequencies that are connected in parallel.Each filter therefore can present a high impedance in its rejection bandwhile combining at, above and below the cutoff frequency to provide aresistive impedance to the common connected source.

FIG. 4 illustrates an example of the first diplexer 222 of theelectrical circuit 220 of FIG. 3. The low pass filter 226, the high passfilter 228, the first terminated low pass filter 256, and the firstterminated high pass filter 260 are shown to each be formed of a varietyof resistors, inductors, and/or capacitors. The capacitor 261 of the lowpass filter 226 and the inductor 263 of the high pass filter 228 can beutilized by the first terminated low pass filter 256 and the firstterminated high pass filter 260, respectively (thus effectively sharinga component) which can minimize the complexity of the electrical circuit220. The second diplexer 224 can also be similarly configured to have ashared capacitor and inductor.

FIG. 5 illustrates an electrical circuit 320 according to anotherembodiment that includes a plurality of diplexers 322 a, 322 b, . . .322 n that are provided in a cascaded arrangement. The plurality ofdiplexers 322 a, 322 b, . . . 322 n can be similar to or the same as thefirst and second diplexers 22, 24 illustrated in FIG. 1. A plurality ofanalog to digital (A/D) converters 364 a, 364 b, . . . 364 n can beelectrically coupled to respective high pass filter outputs 336 a, 336b, . . . 336 n. The low pass output having the lowest cutoff frequency(e.g., 332 n) can also be electrically coupled to the A/D converter 364n. The A/D converters 364 a, 364 b, . . . 364 n can create a compositechannelized A/D converter covering a greater band than an individual A/Dconverter. It is to be appreciated that, in some embodiments, digital toanalog (D/A) converters can be used in lieu of the A/D converters 364 a,364 b, . . . 364 n. In some embodiments, the high pass filter outputs336 a, 336 b, . . . 336 n as well as the low pass output having thelowest cutoff frequency (e.g., 332 n) can be additionally oralternatively connected to frequency mixers creating a channelized downconverter that allows a significant multiplication factor over theeffective bandwidth of conventional technologies.

FIG. 6 illustrates an electrical circuit 420 according to anotherembodiment that includes a plurality of diplexers 422 a, 422 b, . . .422 n that are provided in a cascaded arrangement. The plurality ofdiplexers 422 a, 422 b, . . . 422 n can be similar to or the same as thefirst and second diplexers 22, 24 illustrated in FIG. 1. However, aplurality of matching diplexers 470 a, 470 b, . . . 470 n can beprovided that are electrically attached in a cascading arrangement. Theplurality of matching diplexers 470 a, 470 b, . . . 470 n can beconnected to the plurality of diplexers 422 a, 422 b, . . . 422 n bycoupling each high pass filter output of one of the diplexers 422 a, 422b, . . . 422 n with a corresponding high pass filter output of one ofthe matching diplexers 470 a, 470 b, . . . 470 n with two port switches(indicated by ‘x’). In particular the two port switches from the secondport of the high pass filters of the diplexers 422 a, 422 b, . . . 422 ncan be coupled with the two port switches from the second port of thehigh pass filters of the matching diplexers 470 a, 470 b, . . . 470 n.The last low pass filter from the plurality of diplexers 422 a, 422 b, .. . 422 n and the last low pass filter from the plurality of diplexersplurality of matching diplexers 470 a, 470 b, . . . 470 n can also beconnected together with two port switches. The two port switches can setsuch that the network response can be a low pass, high pass, band pass,band reject, or any combination allowed by the number of diplexers incascade. It is to be appreciated that embedded switching can allow thosesignals falling at the crossover frequency to be routed entirely toeither of the two channels above or below the crossover depending on theswitch state. Without switching, signals falling at the crossoverfrequency are routed equally between the signal paths above and belowthe crossover.

FIGS. 7-16 illustrate different plots depicting the frequency responseof the electrical circuit 420 of FIG. 6 based upon different switchingconditions.

It is to be appreciated that the electrical circuits (20, 120, 220, 320,420) described above can be utilized in a variety of differentelectrical applications. In accordance with one example, the electricalcircuits described above (or a derivation thereof) can be used for highfidelity reception of signals in a densely occupied electromagneticenvironment. Practical active radio circuits have a limited dynamicrange. This dynamic range is usually sufficient for fiber, coax ortwisted pair guided waves absent competing/interfering energy. Howeverthat dynamic range is often insufficient for acceptable operation in adensely occupied (multi-user) electromagnetic environment. It is notuncommon to encounter undesired radio energy a billion times (90 dB)stronger than the signal of interest. These active circuits includeamplifiers, oscillators, frequency mixers, modulators and demodulators.As analog to digital (A/D) converter and digital to analog converter(D/A) technologies advance they are becoming more integral to radiocircuitry. The demand to receive and transmit data at increasinglyhigher rates requires radios to operate with correspondingly increasedinstantaneous bandwidth. A/D and D/A converters, along with digitalsignal processing, are key to enabling operation with increasedinstantaneous bandwidth. Practical active radio circuits, and inparticular A/D and D/A converters require frequency selective filteringto achieve a dynamic range sufficiently for acceptable operation in adensely occupied (multi-user) electromagnetic environment. Filtering isalso required for A/D and D/A converters to avoid frequency aliasingresulting from the discrete time sampling.

In accordance with another example, the electrical circuits describedabove (or a derivation thereof) can be used for coupling radio deviceshaving mismatched frequency coverage such as, for example, in the caseof one broadband antenna to multiple bandlimited radios, multiplebandlimited antennas to a single broadband radio, multiple bandlimitedantennas to multiple bandlimited radios, and/or harnessing multiple A/Dand D/A converters to a common broadband input or output.

In accordance with yet another example, the electrical circuitsdescribed above (or a derivation thereof) can be used as an anti-aliasand reconstruction filter for converting signals between continuous anddiscrete time systems.

The foregoing description of embodiments and examples of the disclosurehas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the disclosure to the formsdescribed. Numerous modifications are possible in light of the aboveteachings. Some of those modifications have been discussed and otherswill be understood by those skilled in the art. The embodiments werechosen and described in order to best illustrate the principles of thedisclosure and various embodiments as are suited to the particular usecontemplated. The scope of the disclosure is, of course, not limited tothe examples or embodiments set forth herein, but can be employed in anynumber of applications and equivalent devices by those of ordinary skillin the art. Rather, it is hereby intended the scope of the invention bedefined by the claims appended hereto.

What is claimed is:
 1. An electrical circuit comprising: a firstdiplexer comprising: a first low pass filter comprising a first inputand a first output, wherein the first low pass filter defines a firstlow pass cutoff frequency; and a first high pass filter comprising asecond input and a second output, wherein the first high pass filterdefines a first high pass cutoff frequency and the first and secondinputs are directly electrically coupled together; and a second diplexercomprising: a second low pass filter comprising a third input and athird output, wherein the second low pass filter defines a second lowpass cutoff frequency; and a second high pass filter comprising a fourthinput and a fourth output, wherein the second high pass filter defines asecond high pass cutoff frequency; wherein: the first output, the thirdinput, and the fourth input are directly electrically coupled together;the first low pass cutoff frequency and the first high pass cutofffrequency are substantially the same; the second low pass cutofffrequency is less than the first low pass cutoff frequency; the secondhigh pass cutoff frequency is less than the first high pass cutofffrequency; and the second low pass cutoff frequency and the second highpass cutoff frequency are substantially the same.
 2. The electricalcircuit of claim 1 further comprising a third diplexer comprising: athird low pass filter comprising a fifth input and a fifth output,wherein the third low pass filter defines a third low pass cutofffrequency; and a third high pass filter comprising a sixth input and asixth output, wherein the third high pass filter defines a third highpass cutoff frequency; wherein: the third output, the fifth input, andthe sixth input are directly electrically coupled together; the thirdlow pass cutoff frequency is less than the second low pass cutofffrequency; the third high pass cutoff frequency is less than the secondhigh pass cutoff frequency; and the third low pass cutoff frequency andthe third high pass cutoff frequency are substantially the same.
 3. Theelectrical circuit of claim 1 further comprising a first terminated lowpass filter comprising a first terminated input that is directlyelectrically coupled with the second output, the first terminated lowpass filter defining a first terminated cutoff frequency that is lowerthan the first high pass cutoff frequency.
 4. The electrical circuit ofclaim 1 further comprising a first terminated high pass filtercomprising a second terminated input that is directly electricallycoupled with the first output, the second terminated high pass filterdefining a second terminated cutoff frequency that is higher than thefirst low pass cutoff frequency.
 5. The electrical circuit of claim 3wherein the first high pass filter and the first terminated low passfilter share an electrical component.
 6. The electrical circuit of claim4 wherein the first terminated low pass filter and the first terminatedhigh pass filter each comprise a singly terminated filter.
 7. Theelectrical circuit of claim 4 wherein the first low pass filter and thefirst terminated high pass filter are connected using a sharedelectrical component.
 8. The electrical circuit of claim 4 wherein thefirst terminated low pass filter and the first terminated high passfilter each comprise a singly terminated filter.
 9. The electricalcircuit of claim 1 further comprising a second terminated low passfilter comprising a third terminated input that is directly electricallycoupled with the fourth output, the second terminated low pass filterdefining a third terminated cutoff frequency that is lower than thesecond high pass cutoff frequency.
 10. The electrical circuit of claim 9wherein the second terminated low pass filter and the second terminatedhigh pass filter each comprise a singly terminated filter.
 11. Theelectrical circuit of claim 9 wherein the second low pass filter and thesecond terminated high pass filter are connected using a sharedelectrical component.
 12. The electrical circuit of claim 9 wherein thesecond high pass filter and the second terminated low pass filter areconnected using a shared electrical component.
 13. The electricalcircuit of claim 1 further comprising a second terminated high passfilter comprising a fourth terminated input that is directlyelectrically coupled with the third output, the second terminated highpass filter defining a fourth terminated cutoff frequency that is higherthan the second low pass cutoff frequency.
 14. The electrical circuit ofclaim 1 further comprising: a first digital to analog converter coupledwith the second output; a second digital to analog converter coupledwith the fourth output; and a third digital to analog converter coupledwith the fifth output.
 15. The electrical circuit of claim 1 furthercomprising: a first frequency mixer coupled with the second output; asecond frequency mixer coupled with the fourth output; and a thirdfrequency mixer coupled with the fifth output.
 16. The electricalcircuit of claim 1 further comprising: a first duplicate and secondduplicate diplexer wherein: the second output is connected to theduplicate second output using a switch; the fourth output is connectedto the duplicate fourth output using a switch; and the third output isconnected to the duplicate third output using a switch.
 17. Theelectrical circuit of claim 1 wherein: the high pass and low passfilters are constructed from ladder networks using series and shuntinductors and capacitors.
 18. The electrical circuit of claim 1 wherein:the second, third and fourth outputs are used as inputs to produce acombined output at the first and second inputs.